Boxelder bugs are flat, oval-shaped insects about half an inch long with a distinctive black and red-orange color pattern that makes them easy to spot. Their most recognizable feature is a pair of red or orange lines running along the edges of the wings, forming a rough “V” shape where the wings overlap on the back. If you’re seeing clusters of dark bugs with red markings on your house or near a tree, you’re almost certainly looking at boxelder bugs.
Adult Boxelder Bug Appearance
Adult boxelder bugs have elongated oval bodies measuring roughly half an inch in length. The overall body color is dark brown to black, with bright red or orange-red markings that set them apart from most other household insects. Three red lines run along the area just behind the head (the pronotum), and the edges of the wings are outlined in red or orange. When the wings are folded flat over the body at rest, those wing edges create a distinctive “X” or “V” pattern on the back.
Their wings are another helpful identification detail. The front half of each wing is leathery and dark, while the back half is membranous and slightly translucent. Underneath the wings, the abdomen is bright red or orange, which becomes visible when the bug flies or is flipped over. They have six dark legs, a pair of segmented antennae about half the length of the body, and a narrow, beak-like mouthpart tucked against the underside of the head.
What Nymphs Look Like
Young boxelder bugs, called nymphs, look quite different from adults. They are smaller, wingless, and primarily bright red or orange-red across the entire body. As nymphs grow through several molts, they gradually develop dark wing pads on their backs and their bodies darken. Early-stage nymphs are almost entirely red and only about 1 to 2 millimeters long, making them easy to mistake for tiny red spiders or mites at first glance. Later-stage nymphs show more black coloring and visible wing buds but still lack the full wings of adults.
If you see small, bright red insects clustered on a tree trunk or near the base of a building in summer, those are likely boxelder bug nymphs. During years with high populations, you can find nymphs on the ground or in gardens feeding throughout the summer months.
Eggs and Where to Find Them
Boxelder bug eggs are small, oval, and yellow when first laid. As the nymphs develop inside, the eggs gradually turn red. Females deposit them in cracks and crevices of boxelder tree bark, on leaves, branches, and occasionally other nearby surfaces. The eggs are laid in small clusters and hatch in 10 to 14 days. You’re unlikely to notice eggs unless you’re specifically inspecting a boxelder tree’s bark up close in spring.
Bugs That Look Similar
A few other insects share the black-and-red color scheme and can cause confusion. The red-shouldered bug (sometimes called the goldenrain tree bug) is the closest look-alike. It’s nearly the same size and shape with red and black coloring, but its red markings are concentrated in broader patches on the “shoulders” behind the head rather than in the thin lines along the wing edges that boxelder bugs display. Red-shouldered bugs also tend to feed on goldenrain trees and chinaberry trees rather than boxelder or maple.
Large and small milkweed bugs also have red (or orange) and black patterns, but their markings appear as bold bands or patches across a wider body, and they’re typically found on milkweed plants rather than clustering on buildings. Stink bugs, particularly the brown marmorated stink bug, share the shield-shaped body and habit of invading homes in fall, but they’re uniformly brown or gray with no red markings at all.
The quickest way to rule out look-alikes: if the bug is black with thin red-orange lines outlining the wings and it’s gathered in large numbers on a sunny wall or near a maple or boxelder tree, it’s a boxelder bug.
Where and When You’ll Spot Them
Behavior is actually one of the best identification tools for boxelder bugs, because they congregate in ways that few other insects do. Starting in mid-July, they gather on female seed-bearing boxelder trees (and sometimes silver maples) to feed and lay eggs. As fall temperatures drop, they migrate toward buildings, seeking out sun-warmed surfaces. They are strongly attracted to buildings with lots of southern or western sun exposure, and structures that stand taller than their surroundings or sit alone on flat ground draw especially large numbers.
In autumn, you’ll see them massed on exterior walls, window frames, and door frames, sometimes by the hundreds. They push into cracks, gaps around windows, and spaces under siding to find shelter for winter. Once inside a home, they’re generally inactive during cold weather. On mild, sunny winter days, though, the warmth can reactivate them, and you’ll find them crawling toward windows and other bright spots indoors. This sudden indoor appearance in the middle of winter catches many homeowners off guard, but the bugs were already inside, just dormant in wall voids or attic spaces until the temperature rose enough to get them moving.
If you’re trying to confirm an identification, the combination of the black body with red wing outlines, the flat oval shape at roughly half an inch long, and the tendency to cluster in large groups on warm, sun-facing surfaces is essentially unique to boxelder bugs in North America.